Side Slip, or Slipping

[2550]

[quote="Colonel Sanders"]

Slips are when the ball falls to the inside of the turn,
as a result of excessive top (outside) rudder. I used
one a couple days ago in a Citabria turning on final, to
slow it down to 55 mph so I could land on a 1000 foot
grass strip. ]]


Just so no youngsters gets the wrong idea; untill you have tens of thounsands of hours like the colonel its much easier and more reliable to get slowed down for shorter than usual strips with a long straight in stabalised approach. A slip is a vital tool to have, but you had better practise it a lot before using it to set up for a short landing.

On another note...I read somewhere that using a slip with much power on produces some unhealthy forces on the prop and airframe. Anyone know for sure if this is true and why?

Im talking about non-areobatic planes here of course, the sort of plane you might want to avoid pulling power to avoid shock cooling, but still need to because you didnt plan your desent far enough back.

[burninggoats]

Imagine if everyone on avcanada acted the same way at the bar as they do here....

Sometimes.... they do.

http://news.nationalpost.com/2012/08/29 ... -pitchers/

[Colonel Sanders]

Thank you for the kind words, but remember that
for every professional, there was once an amateur
that just wouldn't quit

using a slip with much power on produces some unhealthy forces on the prop and airframe.

That could be, but I don't know anything about it,
because I have never slipped with any power on.

When you are high, first thing you do is get the
power all the way off - at least, in a little airplane.
In the C421 and L39, different story.

[schmoo]

I'm glad this thread has been started since it gives me the chance to chime in with a question or two.

1) The colonel stated that he isn't impressed when students attempt to lose speed on final by raising the nose. I am on my second read-through of "stick and rudder" and the author does suggest that during the glide i.e. final , it is a common mistake for new pilots to attempt to steepen their descent by nosing down rather than nosing up, losing speed and steepening the descent that way. He makes little or no mention of slipping, possibly because he appears to be a proponent of rudderless airplanes, or at least, plances without a rudder that can be controlled by the pilot.

So, I guess my question is, is the main reason why raising the nose to lose airspeed on final is not the best choice is because it messes with the glide path or is it simply the more effective manoevre and easier to predict/control ? I assume it's not because the nose up method steepens the glide since the slip would do so as well.

2) Perhaps less interesting, I have always wondered why the altitude decreasing version is called "forward" slip and the other "side" slip. From God's perspective, they look basically the same.

[FlyGy]

2) Perhaps less interesting, I have always wondered why the altitude decreasing version is called "forward" slip and the other "side" slip. From God's perspective, they look basically the same.

The forward slip will change the heading of the aircraft away from the down wing, while retaining the original track (flight path over the ground) of the aircraft.

A forward-slip is useful when a pilot has set up for a landing approach with excessive height or must descend steeply beyond a tree line to touchdown near the start of a short runway. Assuming that the runway is properly lined up, the forward slip will allow the aircraft track to be maintained while steepening the descent without adding excessive airspeed. Since the heading is not aligned with the runway, the slip must be removed before touchdown to avoid excessive side loading on the landing gear, and if a cross wind is present an appropriate side slip may be necessary at touchdown as described below.

The sideslip also uses opposite aileron and rudder. In this case it is entered by lowering a wing and exactly enough opposite rudder so the airplane does not turn (maintaining the same heading), while adding airspeed as required.

In the sideslip condition, the airplane's longitudinal axis remains parallel to the original flightpath, but the airplane no longer flies straight along its original track. Now, the horizontal component of lift forces the airplane to move sideways toward the low wing.

A sideslip is also one of the methods used by pilots to execute a crosswind landing. In order to land crosswind using the sideslip method, the pilot puts the airplane into a sideslip toward the wind to maintain runway centerline position while maintaining heading on the centerline with the rudder, touching one main landing gear, followed by the second main gear, and finally the nose gear (or tail gear if employed). This allows the wheels to be constantly aligned with the track, thus avoiding any side load at touchdown.

[Colonel Sanders]

raising the nose to lose airspeed on final is not the best choice is because it messes with the glide path

Correct. You started out on the correct glidepath but too fast.

You pull back and convert your excess airspeed to altitude. You
are now at the correct airspeed, but too high. You haven't addressed
the root cause of the problem - you have too much energy. All
you have is transformed your excess energy problem from too
much airspeed, into too much altitude.

What you could do now is nose down, back down to the correct
glidepath. This will convert your excess altitude back into excess
airspeed.

Converting your energy from one form to another really isn't
helping you a whole lot. You need to get rid of your excess
energy. You do that by reducing power to idle, applying more
flaps (if you can), and then sideslipping. If that doesn't do it,
you are totally screwed. Just overshoot, get set up and come
around and try again.

PS C172 does marvellous slips with flaps. Disregard any
nonsense you are told about it.

I am on my second read-through of "stick and rudder"

People love that book, but I don't quite know why. It was
written a very long time ago, by an author who had some
pretty peculiar ideas. At the time I guess it was ok.

“The important thing to understand about the rudder pedals is that they are unnecessary; like your wisdom teeth, they serve no very good purpose but can cause much trouble. The airplane needs no rudder pedals. It should have no rudder pedals. In all probability it will have no rudder pedals 10 years hence.”

Blasphemy!







Pure poetry in motion!

[iflyforpie]

Actually, pitching up to reduce airspeed is very effective. Most people see the airspeed converted to altitude (kinetic-potential) and then give up and pitch down again. If you hold it at the absolute minimum approach speed with no power and full flap, you will most likely need power before you land unless you couldn't see the numbers to begin with.

I guess the point I am trying to make is that if your airspeed is too high, slipping alone might not be enough. First get your airspeed, then worry about how you will lose your altitude (power, flaps, slipping, etc).

Another thing a lot of people don't notice is how power affects airspeed. Chop the throttle, and on most light aircraft you will actually speed up. Dragging in with power, you will most likely be fighting to keep airspeed up. On a go around this is very noticeable unless you dial in a whole pile of nose down trim.

Anticipating that if you are high and chop power that your trimmed airspeed is going to rise helps you manage energy.

But if you have too much energy, by all means slip it on. I'm sure more people have died from logbook paper cuts than slipping a 172 with flaps.

[Beefitarian]

I'm with you colonel but he's right the rudder is not needed. I even took some pictures just for you at Oshkosh of a guy with his foot flat on the floor in the red bird piper cub simulator.


Notice the foot position.



And here's a shot of the ball.




I flew it next and his landing was better than mine.
I can't feel the thing yawing.

[Colonel Sanders]

If you hold it at the absolute minimum approach speed with no power and full flap, you will most likely need power before you land

Taking it all the way up the back side of the power
curve is a pretty sporty way to approach. The
exponentially increasing induced drag will help, I
suppose, but this is a very very advanced technique,
which I don't recommend.

But if you have too much energy, by all means slip it on

Typically this occurs on a flight test forced approach
where the student has not flown a large enough circuit
and as a result is ridiculously high. All he can do at
that point is power off, full flap, forward slip with
full rudder and hope for a "2".

Not the best technique, either. Best to overshoot
(if you have an engine) and try again.

[Learning2Fly]

Awesome stuff everyone! This discussion reveals the benefit of asking questions
of experienced individuals, rather than blasting through a web article, and hoping to make sense of the content.

Based on what I know about stall, I'd be hesitant to try a low power, low speed approach
with the nose up. I guess with experience, and knowing the aero limits/response
of your aircraft,, a pilot would not think twice about pushing the envelope. I'd be scared
of dropping out of the sky with too little altitude, and power to recover.

[schmoo]

I guess the point I am trying to make is that if your airspeed is too high, slipping alone might not be enough. First get your airspeed, then worry about how you will lose your altitude (power, flaps, slipping, etc).

I can see the merit of this, but for those occasions where there is not enough time to do both, that is where I would think the forward slip really shines, as long as you are in a plane that will let you slip aggressively. About a month ago, I flew to Oshawa airport and being unfamiliar with it, I was quite high on final. I guess my instructor's advice actually stuck with me. I did the most aggressive slip I could and lost almost all the altitude I needed. Felt like I was landing on a heli-port. I felt really good about it since airspeed was never an issue and I was prepared for the go-around if need be. Please understand, I am a low hour pilot, easily amused and by no means bragging.

Another thing a lot of people don't notice is how power affects airspeed. Chop the throttle, and on most light aircraft you will actually speed up. Dragging in with power, you will most likely be fighting to keep airspeed up. On a go around this is very noticeable unless you dial in a whole pile of nose down trim.

Would you say that the increase in airspeed isn't a direct result of chopping power ( cuz that would seem a little strange ) but is because after chopping power, the plane wants to nose down to maintain it's AOA and most pilots would tend to let it do just that ?


Lastly, a question about slipping turns in the final. Is there any actual risk to stalling the high wing if the slipping turn is too aggressive or as long as your airspeed is good is the risk is negligible ? It makes sense that since you are descending the risk is reduced, but perhaps an error in glide angle or airspeed could catch a low-time pilot offguard ? Again, I think reading "stick and rudder" has got me overthinking a number of things.

[slam525i]

PS C172 does marvellous slips with flaps. Disregard any nonsense you are told about it.

I always thought that slipping with the flaps down affects airflow over the elevator, and I have experienced that with the yoke fighting back, not smoothly but in pulses. Am I incorrect?

Also, I remember reading in Flying mag a long time ago that by reducing pitch, you're flying at a less "efficient" AOA and the additional drag from additional speed helps waste energy, and the author (I can't remember who) advocated nosing down rather than hang the airplane at a low speed, high AOA to bleed off altitude.

It seems to me that flying faster or slower both reduce your energy by the time you're over the button. Both have their risks, either from excess speed or from getting on the backside of the curve. Me? I prefer slipping. Lots of it. I think I subconsciously fly circuits tighter than they should be, just so I have and excuse to kick the rudder in.

[Colonel Sanders]

Is there any actual risk to stalling the high wing if the slipping turn is too aggressive

No. Slips are good, skids are bad. I might suggest that you get the
nose down in the slip, to maintain your airspeed as the drag of the
side of the fuselage builds. I regularly do 90 degree banked slips on
final.

re: slips w/flaps in 172 ... this is NOT a control issue. The only issue
is that the pilot might get upset by the possible pulsing of the elevator
and do something dumb. If the pilot doesn't panic and do something
dumb, a 172 slips bloody marvellously with flaps!

[2550]

Plus that "pulsing" prob gives you a good preveiw of what a tailplane stall might feel lile.

[Colonel Sanders]

I think I subconsciously fly circuits tighter than they should be

Objectively it is a good idea to fly a circuit with the downwind close enough
to the runway, and slightly high on base and final, so that if your engine
failed, you could glide to the runway. Obviously with ATC, other traffic,
etc this isn't always possible, but you might be surprised how I deal
with that, to avoid becoming power dependent.

A friend of mine had his tri-pacer's engine fail turning base. Good thing
he was close enough to make the runway, otherwise it might have
been ugly.

More than once in the winter, I have seen the prop stop on airplanes
(without me in it!) on final. Unsettling.